The concept is:

That embarrassed feeling one has when uncertain if they have just spoken a thought out loud, usually while deep in thought in a public space.

Is there a word or phrase for this?

If not, I just posted a call to invent one on my blog. All contributers would be very welcome. Here's the link:

http://intimationsofubiquity.blogspot.com/2007/03/language-did-i-just-say-that-out-loud.html

I hope someone can put me on the right track. Thanks to Anu and all of you for existing.